Plasma device including plasma injection structure and method



4, 1970 TIHIRO OHKAWA ET AL 3,523,209

PLASMA DEVICE INCLUDING PLASMA INJECTION STRUCTURE AND METHOD Filed June29. 1967 3 Sheets-Sheet 1 FIG! . I ARTHUR A.SCHUPP BY b va emnflumslqfim, ATTORYEYS g- 1970 TIHIRO OHKAWA ET AL PLASMA DEVICE INCLUDINGPLASMA INJECTION STRUCTURE AND METHOD Filed June 29. 196'? 3Sheets-Sheet 2 new wrraou'r muccroa INJECTKON onzecnon OUTSIDE WALL newwn-H mucaoa yon: Axls I N5! DE HALL CENTiMETEES ARTHUR A. SCHUPP I400 I.-'\I"TUR.\TEYS 250 400 eofiMiao I000 I200 I330 5v flay WW4,

g- 4, 1970 TIHIRO OHKAWA ETAL 3,523,209

PLASMA DEVICE INCLUDING PLASMA INJECTION STRUCTURE AND METHOD Filed June29. 196! 3 Sheets-Sheet 5 1 "P TIMING CIRCUITS J A l A I9ZA X IQAA 0 35mafia/weal I886 F 1 5 b4 INVENTOR TIHIRO OHKAWA ARTHUR'A. SCHUPP UnitedStates Patent 3,523,209 PLASMA DEVICE INCLUDING PLASMA INJEC- TIONSTRUCTURE AND METHOD Tihiro Ohkawa and Arthur A. Schupp, In, San Diego,

Calif., assignors, by mesne assignments, to Gulf General AtomicIncorporated, San Diego, Calif., a corporation of Delaware Filed June29, 1967, Ser. No. 650,006 Int. Cl. H01j 1/50, 17/26; H01h 1/02 US. Cl.315111 19 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus forinjecting plasma into a confining magnetic field is provided with whichthe confining field is eliminated adjacent the entry point during thetime while the plasma is injected and is reinforced adjacent the entrypoint at other times. The plasma may also be guided to the entry pointusing one form of the method and apparatus.

This invention relates generally to methods of and apparatus formanipulating plasma and, more specifically, to an improved device withwhich a plasma may be injected into plasma confining magnetic fields andan improved method of injecting plasma into such fields.

In recent years methods and apparatus have been developed for producing,manipulating and confining electrical plasmas, which plasmas are ionizedgases comprising approximately equal numbers of positively charged ionsand free electrons at high temperatures. Such plasmas may be utilized assources of electrons for electron beams which in turn may be used inprocessing, forming or joining materials as well as in a variety ofother useful applications. Plasmas may also be utilized to producepositive or negative ion beams which may be used, for example, to cleanor etch surfaces without destructive heating. In addition, if a plasmais formed from a suitable gas such as deuterium or a mixture of gasessuch as deuterium and tritium, fusion reactions may occur within theplasma body. Such fusion reactions may produce highly energized protonsor neutrons or other particles, thus providing a source of neutrons orprotons or such other particles at high energy. If the proper conditionsare realized, the energy obtained from the fusion reactions may exceedthe input energy and provide useful power.

In order to achieve many of these results, it is necessary to provide asuitable means of confining the plasma in a given region at hightemperature for an appreciable period of time. Such confinement ofplasma is difficult to achieve with ordinary solid walled containers,since contact of the plasma ions with the walls of such a containercools the plasma. Consequently, external magnetic fields having avariety of configurations have been utilized to confine the plasma in aselected space. In some systems an un-ionized gas is injected into theconfinement space and therein ionized to produce the plasma, but in manysystems it is preferred first to produce the plasma outside, then toaccelerate it into the confinement space through an injection window oraperture and finally to trap it there by means of the magnetic fields.

Injection of plasma into a confining field presents certain problems,however. Charged particles moving in a magnetic field tend to bereflected from regions of higher than average field strength. A magneticfield which is strong enough to confine the plasma ions may also bestrong enough to exclude ions which are propelled toward the field.Conversely, plasma ions which have sufiicient energy to penetrate intothe confinement space will also tend to immediately escape therefrom.The problem is aggra- 3,523,209 Patented Aug. 4, 1970 ice vated by thefact that magnetic field configuratidns providing relatively stableconfinement of plasma are usually strongest at the periphery of theconfinement space so that the equilibrium position of the plasma is atthe center of the space. As a result, the plasma accelerated toward sucha confining field must pass through a region of increasing magneticstrength and through the region of the strongest magnetic field to enterthe confinement space.

Penetration of plasma into a confining field in some cases is aided bythe creation of a polarization of charge in the plasma being injecteddue to motion of the plasma transversely of the magnetic field. Thispolarization causes a local electric field in the plasma which istransverse to the magnetic field and in turn results in a drift velocityof the plasma into the confining field. The plasma will nevertheless bedecelerated as it moves into the magnetic field because the plasma isnot a perfect conductor and the separation of charges which causes thedrift velocity is not complete. Hence the drift velocity in manyinstances is not great enough to overcome the plasma excluding effectsof the magnetic field to confine the plasma. As a result the enteringplasma stagnates without reaching the center of the confinement spaceand may interact with the solid members of the device creating themagnetic field to produce a gas cloud near the point of entry.

In the present invention the problem of injection of plasma into anconfining field is solved by creating a component of magnetic field inthe confinement space adjacent the injection window, which component offield momentarily suppresses the confining field so that the plasmapropelled through the window can enter the confinement space. After theplasma has entered the space, the confining field is restored adjacentthe injection aperture so that the plasma will not leak out of theconfinement space along the path by which it entered.

It is therefore an important object of this invention to provide animproved method of and apparatus for injecting plasma into a plasmaconfining field.

Another object of the invention is to provide an improved method of andapparatus for suppressing a plasma confining field in the path of plasmabeing injected into a confinement space.

Still another object of the invention is to provide an improved methodof and apparatus for maintaining a magnetic confining field adjacent tothe plasma injection aperture during periods when injection is nottaking place.

A further object of the invention is to provide an improved method ofand apparatus for momentarily suppressing a plasma confining fieldduring plasma injection and for subsequently restoring such field.

A still further object of the invention is to provide a method andapparatus for injecting plasma into a plasma confining field in whichthe amount of interaction of the injected plasma with portions of theapparatus is optimized.

Yet another object of the invention is to provide an apparatus forinjecting plasma into a confining field which can guide the plasma andsuppress or reinforce the confining field as desired.

Other objects and advantages of the invention will become apparent fromthe following description when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic perspective 'view of a plasma apparatus withwhich the present invention may be utilized with portions being brokenaway to show certain features thereof;

FIG. 2 is an enlarged diagrammatic perspective view of a portion of theapparatus shown in FIG. 1 showing various features of the invention;

FIG. 3 is a graph showing the magnetic field configuration as a functionof distance from the injection aperture at two different times;

FIG. 4 is a circuit diagram of the apparatus shown in FIGS. 1 and 2;

FIG. 5 is a graph showing the magnetic field near the injection apertureas a function of time;

FIG. 6 is an enlarged diagrammatic view of another form of a portion ofthe apparatus shown in FIG. 2; and

FIG. 7 is a diagram of a circuit adapted for use with the apparatusshown in FIG. 6.

Generally, as shown in the drawings, a plasma apparatus with which thepresent invention may be utilized includes a vacuum sealed casing 10within which is positioned means 12 for producing a plasma confiningmagnetic field within the casing. The invention may be utilized inconjunction with a variety of such apparatus but for clarity and ease ofdescription it will be described in conjunction with the specificillustrated apparatus.

In the structure illustrated in FIG. 1, the vacuum sealed casing 10 isin the shape of a toroid and formed of a conductive material such ascopper. It encloses, in spaced relationship and suitably insulatedtherefrom, a toroidal jacket 13. The jacket, in turn, encloses aplurality of endless rods or members 15, of conductive material such ascopper, spaced about the minor circumference of a toroidal confinementspace 16. The jacket 13 is internally fluted or corrugated around itsminor circumference to provide a plurality of alternate ridges 17 andgrooves 18 each of which extends around the major circumference of thejacket. One each of the rods is received in each groove 18 in spacedrelationship to the wall thereof. A current is induced in each of therods in the direction of the arrow 19 by a power source 20, ashereinafter described in detail. When a current passes longitudinallythrough each rod 15, an oppositely directed current in the direction ofthe arrow 21 is induced in the jacket 13. These currents in combinationprovide a magnetic field in the confinement space 16 which is concavebetween the rods 15 and the wall of the grooves 18 and convex in thespace adjacent the ridges 17 relative to the minor axis of the toroidalconfinement space. Plasma is injected into the space 16 through a windowor aperture 22 in the jacket 13.

As previously indicated, current is induced in each rod 15 and, in turn,in the jacket 13 by a power source 20. As shown in FIG. 1, the powersource includes a toroidal core transformer 38 which is disposed so thatthe rods 15 pass through the center hole or major axis thereof, andthereby act as short circuited secondary windings of the transformer.The transformer 38 includes a core 40 of iron laminations, and a primarywinding or coil 42 of wire wrapped about the core 40. The primarywinding 42 of the transformer 38 is connected to a source of pulsatorypower such as will be described in detail below.

As also shown in FIG. 1, the transformer is provided with a toroidalhousing 44 of conductive material, such as copper, which is disposedabout the primary winding 42. An annular gap 46 is provided in thehousing 44 adjacent the major axis thereof. The transformer housing 44is suitably insulated from the casing 10 and is connected to atransverse gap 47 in the jacket 13 by a pair of spaced apart flanges 48of conductive material, such as copper, which extend between the ends ofthe jacket 13 and the ends of the transformer housing 44. By this meansthe jacket is prevented from acting as a shorted turn of the transformerand hence from excluding magnetic flux from its interior so that currentmay be induced in the rods 15.

Because of the toroidal shape of the apparatus, the rods 15 havedifferent lengths or major circumferences. When a current is passedthrough the primary winding 42, each rod 15, because it is a shortedturn of the transformer, generates the same magnetic flux. Therefore,the

current density required in the jacket 13 around the short rods 15 ishigher than the current density required in the jacket wall 13 aroundthe longer rods. If the proper current density is not available locallyto match the current density required, a transverse magnetic field willbe set up at the gap 47 between the ends of the jacket 13. Therefore,the turns of the primary winding 42 are preferably distributed on thecore 40 so that the flow pattern of the currents on the surface of theflanges 48 goes generally directly in toward the grooves 18 whichsurround the longer rods and does not cross the whole flange 48 to thegrooves 18 surrounding the shorter rods 15.

Preferably, to insure proper distribution of the current, the gapbetween the flanges 48 is tapered toward the major axis of theconfinement space 16 so that the width of the gap is inverselyproportional to the distance of the point on the flange 48 from themajor axis of the toroid. Moreover, perforations 50 are preferablyprovided in the flanges 48 to aid in the proper distribution of currentflow on the surface of the flanges 48.

So that plasma trapped in the confinement space does not exchange itscharge with neutral gas, and thereby cause hot ions to be neutralizedand escape across the magnetic confining fields, the plasma region 16 ismaintained at as high a vacuum as possible (i.e., as free as possiblefrom neutral atoms and molecules). In the illustrated embodiment, means52 such as a conventional vacuum pump is connected to the casing 10 forrapidly evacuating the plasma region. In this connection, a substantialnumber of small apertures 53 are provided in the jacket 13 providingcommunication between the space enclosed by the casing 10 and the spaceenclosed by the jacket 13.

As best shown in FIG. 2, plasma is injected radially into theconfinement space 16 by means of a source 58 of plasma, which mayinclude a conventional plasma gun 60. Preferably, the plasma source 58includes purifying apparatus 62 for trapping neutral particles andpreventing them from entering the casing thus purifying the plasmabefore it enters the jacket. A suitable device for performing suchpurification is described in co-pending application Ser. No. 408,949, ofFranklin R. Scott, et al., entitled Plasma manipulation method andapparatus, now Pat. No. 3,445,722, filed Nov. 11, 1964, and assigned tothe assignee of the present invention.

It will be apparent that in order for the confining mag netic field toexist at its peak strength when the plasma reaches the confinement spaceit is necessary to initiate the confining magnetic fields prior to thetime of injection. To enable the purified plasma to enter the magneticfields, a plasma injection device 64 is provided adjacent the injectionwindow 22.

The injection device as illustrated in FIG. 2 includes a cylindricalinjection tube or pipe 66 which is connected at its outer end to theplasma source 58, extends through the wall of the casing 10, andterminates at the window 22 in an annular inner face 68 adjacent to theinner wall of the jacket 13. Although it is not necessary that the tubebe such, the face 68 of the injection tube is formed of a conductivematerial such as copper and is connected to conductor plates 70 and 72which are perpendicular to the axis of the tube 66 and parallel to themajor circumference of the toroid 13. Each plate 70 and 72 is connectedat its outer end to a conductive member 74 and 76, respectively, whichextend away from the jacket 13 parallel to the axis of the tube 66. Themember 76 is connected at its outer end to a conductive annulus 78 whichis spaced from and surrounds the tube 66. The annulus 78 and the outerend of the member 74 are connected to the respective terminals of acoaxial cable 80 connected to a direct current power source through acircuit to be described below. (FIG. 4).

The entire assembly of the injection device may be securely fastened tothe jacket 13 and the casing 10 by potting with a suitable epoxy resin81 around the outside of the tube 66 so as to completely fill theinjection aperture 22 outside of the end 68 of the pipe 66. A layer ofstainless steel foil 82 covers the epoxy resin to prevent the epoxyresin from accumulating a charge or evaporating into the confinement 16space and contaminating the plasma. It also provides a continuousconductive surface at the inner surface of the jacket 13 except for theend of the tube. It will be apparent that current supplied through thecoaxial cable 80 will flow along the member 74 and the plate 70 to theface 68 of the pipe 66 where it will divide and fiow across the face 68by going around both sides of the end of the pipe. The divided currentwill reunite in the plate 72 and fiow through the member 76 and annulus78 back to the coaxial cable. The direction of flow may, of course, bereversed.

The effect of this current on the magnetic field in the portion of theconfinement space 16 adjacent the window 22 depends upon the directionof the current around the face 68 in relation to the current induced inthe jacket 13. When these currents are in generally opposite directionsas shown by arrows 79 on the face 68 and arrow 21 on the jacket in FIG.2, the confining magnetic field will be diminished due to the componentof magnetic field caused by the current around the face. When thecurrents are in generally the same direction, the confining field willbe increased due to the component of magnetic field caused by thecurrent around the face. These effects are shown in FIG. 3, which is agraph of the magnetic field strength taken along the axis of the tube 66extended from the window to the irmer wall of the jacket 13. The solidline shows the field when the currents in the jacket 13 and on the face68 are in generally the same direction while the dashed line shows thefield when the currents are in generally opposite directions.

In operation of the apparatus, the confining magnetic field is firstinitiated. This field is then momentarily suppressed by operation of theinjection device at approximately the same time that plasma which hasbeen ac celerated along the pipe 66 from the plasma source 58 reachesthe inner wall of the jacket 13. After the plasma has entered theconfinement space, the confining field adjacent the window is restoredand reinforced by the injection device. This mode of operation isaccomplished by means of the circuit shown in FIG. 4.

In the illustrated circuit the rods 15 are linked through thetransformer 38 and an ignitron bank 83 to a capacitor bank 84. A secondignitron bank 86 is connected across the primary 42 of the transformer38 and functions to short circuit the primary of the transformer after apredetermined time so that the confining magnetic field will decay. Theprimary 42 of the transformer 38 and the capacitor bank 84 and ignitronbank 83 are also connected to the injector device 64 through suitableinductors 88 and 89 which are in series connection on each side of theinjection device. An injection capacitor bank 90 in series with aninjector ignitron bank 92 and a suitable resistor 94 is connected acrossthe injection device. The ignitron banks 83, 86 and 92 are .fired at thedesired times relative to the time of plasma injection by timingcircuits 96, which may be conventional. The polarities of the charges onthe capacitors 84 and 90 and the connections to the transformer 38 andthe injection device 64 are so arranged that the current in the face 68caused by discharge of the injection capacitor bank 90 is opposite tothat produced in the jacket 13 by discharge of the capacitor bank 84.

In operation of the apparatus the capacitors 84 and 90 are charged withthe polarities shown by conventional direct current power supplies .(notshown). These capacitors may be charged through switching means whichare opened when the capacitors are charged to the desired potential. Thetiming circuits 96 are then started by some initiating signal, which maybe the closing of a switch. The timing circuits 96 thereupon apply acontrol signal to the ignitors of the ignitron bank 83 which is therebyrendered conductive.

The capacitor bank 84 discharges through the ignitron bank 83 so as tocause current flow through the primary 42 of the transformer 38 and alsothrough the inductor 89, the injector device 64 and the inductor 88. Asaresult, the currents in the jacket 13 and face 68 flow in the samedirection and the magnetic field adjacent the window 22 rises to a peakas shown in FIG. 5 and begins to decay.

The rise in the field represents a transfer of energy from the chargedcapacitor 84 to the field produced by the transformer 38. The peak inthe field represents the completion of the transfer and signifies thecomplete discharge of the capacitor 84. At about this point in time, acontrol signal is supplied by the timing circuits 96 to the ignitor ofthe ignitron bank 86 which thereupon shunts the capacitor 84 and theignitron bank 83. This leaves the capacitor 84 discharged, while currentcontinues to circulate in the winding 42 until the energy is dissipated.

At the same time that energy is transferred to the winding, part of theenergy in the capacitor 84 is transferred to the fields of inductors 89and 88 and the injector device 64 so that current also continues tocirculate through the injector device 64 upon actuation of the ignitronbank 86.

Shortly after the ignitron bank 86 is fired, the timing circuits 96supply a control signal to the ignitron 92. The injector capacitor bank90 is then discharged by the injector ignitron bank 92 so as to causecurrent to flow through the resistor 94 and through the injector 64 inthe direction opposite to the current in the injector 64 caused bydischarge of the capacitor bank 84. This results in a component ofmagnetic field adjacent the window 22 which opposes and tends tosuppress the field created by the currents in the jacket 13. The effectof the combined components of magnetic field is a momentary suppressionof the field adjacent the window as shown in FIG. 5, so that plasmaaccelerated through the window 22 can enter the space 16.

The discharge of the capacitor 90 is isolated from the rest of thecircuit by the inductors 88 and 89. Because there is little inductancein the discharge path for this current, there is little tendency tooscillate, and further oscillation is damped by the resistor 94. Theremay be a slight overshoot as shown in FIG. 5. Resistor 94 also serves todetermine the time constant with which the capacitor 90 discharges andhence the duration of the current pulse through the injector 64.

Even after this current is dissipated, the current in the inductors 88and 89 that was caused by discharge of the capacitor bank 84 continuesflowing in the same direction in the face 68 as the current in thejacket 13 and causes a component of field adjacent the window which isin the same direction as and reinforces the confining field.

In one particular mode of operation the parameters of the circuit are sochosen that the confining field rises to a peak in 400 sec. Thetransformer is shorted 500 1. sec. after initiation of the currentthrough the rods. This confining field has a decay time constant ofabout 5,500/L sec. About 50 sec. after the primary is shorted the plasmais injected and the injection capacitor bank 90 is discharged so as tocreate a field component opposed to the confining field adjacent theinjection window 22. The confining field is suppressed for approximately20a see by this opposing field component. The persisting portion of thefield produced by the currents in the injection device as produced bydischarge of the capacitor bank 84 is in phase with and in the samedirection as the confining field produced by the current in the jacket13 and reinforces the latter field adjacent the injection window 22 asboth field components decay. The resulting time dependence of the totalfield adjacent the window 22 is shown in FIG. 5.

In one embodiment of plasma research apparatus, a copper jacket 13having a wall, 3 cm. thick, is formed so as to provide six ridges 17 andsix grooves 18. The wall is perforated so that approximately 25 percentof its area is open and the jacket is disposed within a copper casing10. The ridges are made with a radius of 15 cm., and the grooves aremade with a radius of 28 cm. Six oval shaped rods 15 are disposed in thegrooves. The radius of the larger arcuate portion of each rod is 22 cm.,and the radius of the smaller arcuate portion of each rod is 15 cm. Theprojection of the flat sides of the rods on the diameter is 7 cm., and aone cm. gap is provided between the flat side of the rod 15 and thejacket 13. The copper pipe 66 has an inner diameter of cm. and thewindow 22 is 12 inches in diameter.

The capacitor bank 84 is charged by an external power source so that aflux density of 15,000 gauss is created in the core of the transformer,and the length of the current pulse is 0.1 second. The confinement space16 is maintained at a vacuum of mm. Hg. Preferably, a plasma density of10 particles per cubic cm. is provided.

The capacitor bank 84 has a capacitance of 7,200 f., while the injectioncapacitor bank 90 has a capacitance of 150 mf. The peak flux densityadjacent the jacket 12 is 5,000 gauss. The resistance of resistor 94 ismilliohms and the inductance of inductors 88 and 89 are each 10 ,uH.

Although the injection device 64 illustrated in FIG. 2 is highly usefulin many applications and provides for greatly improved injection of lowenergy plasma, it has been found in practice that a gas cloud may beproduced near the injection window which can contaminate the plasma.Such a gas cloud, it is believed, may be produced by interaction of theinjected plasma with the inner surface of the injection tube 66.Accordingly, in the embodiment illustrated in FIG. 6 means are providedfor producing a longitudinal magnetic field in the tube which serves toguide the plasma along the center of the tube and prevent interaction ofplasma with the tube surface.

Specifically, as shown in FIG. 6, the injection device is divided intotwo portions 164A and 164B which are in- I sulated from one another andprovide two separate but interconnected current paths. The deviceincludes a cylindrical injection tube 166 having an upper portion 166Aand a lower portion 166B substituted for the tube 66 of FIG. 2. Theportions 166A and 166B are insulated from one another by electricalinsulation 167 and terminate at the window 22 in semi-annular innerfaces 168A and 168B, respectively. On each portion 166A and 166B, anoverlapping sheet 169A and 169B is provided which masks the gap betweenthe portions and fits into a mating depression in the inner surface ofthe other member so that the inner surface of the tube is cylindrical.The face 168A of upper portion 166A is connected to conductor plates170A and 172A which are perpendicular to the axis of the tube 166 andare parallel to the major circumference of the toroid 13. Similarly theface 168B of lower portion 166B is connected to conductor plates 170Band 172B which are parallel to and insulated from the plates 170A and172A.

The plates 170A, 170B, 172A and 172B are each connected at their outerends to respective conductive members 174A, 174B, 176A and 176B, whichextend away from the jacket 13 parallel to the axis of the tube and areeach insulated from the adjacent member. The outer ends of the members176A and 176B are connected to a conductive annulus 178 which is spacedfrom and surrounds the tube 166. The annulus 178 is divided into a semicircular lower portion 178A and an upper portion 178B which areinsulated from one another. The member 176A is connected to the lowerportion 178A of the annulus by means of a connecting member 179 whilethe member 176B is directly connected to the upper portion of theannulus 178B. The end of the lower portion 178A of the annulus oppositethe member 176A and the outer end of the member 174A are connected tothe respective terminals of a coaxial cable 180A connected to a directcurrent power source through a circuit to be described below (FIG. 7).Similarly the end of the upper portion 178B of the annulus opposite themember 176B and the outer end of the member 176A are connected through acoaxial cable 1808 and to the power source.

It will be apparent that current supplied through the cable 180A willflow along the member 174A and the plate A, the pipe portion 166A, theplate 172A, the member 176A, the vertical member 179, and the lowerportion 178A of the annulus back to the axial cable. This fiow isindicated by solid arrows. Similarly current supplied through the cableB will flow along the various elements 174B, 170B, 166B, 172B, 176B, and178B back to the cable. This flow is indicated by dashed arrows. Sincethe entire tube 166 is formed of a conductive material the current flowin each case is around the entire tube portion 166A or 166B rather thanjust the face pOrtiOns 168A and 168B. Hence, a magnetic field is createdin the tube itself as well as at its face. Where the respectiveoverlapping sheets 169A and 169B are mated with the opposing portion166B and 166A, respectively, an image current will be induced in thesheets which will have the same direction as the primary current on theinner surface of the tube. Thus the current distribution on the innersurface of the tube is made more uniform since the sheets cover theinsulated gaps between the tube portions.

When the current in each of the members 174A and 1748 has the samedirection the eifect on the magnetic field in the portion of theconfinement space adjacent the window will be approximately the same asin the embodiment of FIG. 2. That is, when the currents across the faceare generally opposite to the currents induced in the jacket 13, theconfining field is diminished and when such currents are in the samedirection as those in the jacket the field is strengthened.

The current direction in either of the annular portions may, however, bereversed so that there is an effective closed current loop around thetube. Such a loop creates a longitudinal magnetic field which forces theplasma toward the center of the tube away from the tube surfaces andhelps guide it. As a result there is less interaction between the plasmaand the tube to create a gas cloud. Similar results may be achieved bysimply having different magnitude currents in each portion of theannulus as well as by a change in their directions. Of course, in such acase the confinement field will not be completely canceled. Thisdeficiency, however, in practice may be out-Weighed by the lessening inthe amount of contaminating gas produced.

The embodiment of FIG. 6 may be operated by the circuit of FIG. 7. As inthe previous embodiment the rods 15 are linked through the transformer38, and the ignitron bank 83 to a capacitor bank 84. A second ignitronbank 86 is connected across the primary 42 of the transformer 38 andfunctions to short circuit the primary of the transformer after apredetermined time so that the confining magnetic field will decay. Theprimary 42 of the transformer 38 and the capacitor bank 84 and ignitronbank 82 are also connected in series to the injector device 164 throughsuitable inductors 188A and 188B on one side and inductors 189 on theother side. Inductors 188A and 188B are in parallel with one another andin series with the respective portions of the injector 164A and 164B. Aninjection capacitor bank 190A in series with an injector ignitron bank192A and a suitable resistor 194A is connected across the portion of theinjection device 164A. Similarly an injection capacitor bank 190B inseries with an injector ignitron bank 192B and a suitable resistor 194Bis connected across the other portion 164B. The ignitron banks 83, 86,192A and 192B are fired at the desired times relative to the time ofplasma injection by timing circuits 96, which may be conventional. Thepolarities of the charges on the capacitors 84, 190A and 1908 and theconnections to the transformer 38 and the injection device 64 may be soarranged that the current in the faces 168A and 168B caused by dischargeof the injection capacitor banks 190A and 190B is in the same generaldirection and opposite to that produced in the jacket 13 by discharge ofthe capacitor bank 84. The current in either portion 164A or 164B may bereversed by manually disconnecting at the points marked A or at thosemarked B and reversing the leads. The same result may be accomplished byswitch means.

In operation of the apparatus the capacitors 84, 190A and 190B arecharged with the polarities shown by conventional direct current powersupplies (not shown). These capacitors may be charged through switchingmeans which are opened when the capacitors are charged to the desiredpotential. The timing circuits 96 are then started by some initiatingsignal, which may be the closing of a switch. The timing circuits 96thereupon apply a control signal to the ignitors of the ignitron bank 83which is thereby rendered conductive.

The capacitor bank 84 discharges through the ignitron bank 83 so as tocause current flow through the primary 42 of the transformer 38 and alsothrough the inductors 188A and 188B, the portions of the injector device164A and 164B and the inductor 189. As a result, the current in thejacket 13 and the faces 168A and 168B flow in the same general directionand the magnetic field adjacent the Window 22 rises to a peak as shownin FIG. and bgeins to decay. If the direction of the currents in thetube 166 are such as to form a closed loop this elfect will be reducedsince the current in one face 168A or 168B will be opposite to thedirection of the jacket current but a longitudinal guiding field willalso be created in the tube. Reversal of the current in both parts ofthe tube as described in connection with the previous embodiment willreverse the direction but not the overall effect of the guiding field.

It should be realized that while the structure shown and described aboveis a toroidal construction, certain features of this invention may beemployed in a linear or other geometrical form of plasma device.Moreover, instead of having the current induced in the rods by theillustrated circuits the rods may be separately excited by parallelleads extending through a wall of the jacket. In such a case, localmagnetic fields generated about the parallel leads guard or protect theleads from the hot plasma.

Various other changes and modifications may be made in the abovedescribed plasma apparatus without deviating from the spirit or scope ofthe present invention, various features of which are set forth in theaccompanying claims.

What is claimed is:

1. A method of injecting plasma into a space wherein a plasma confiningmagnetic field exists comprising the steps of accelerating the plasma ina path toward the space, momentarily suppressing the confining field inthe path of the plasma so that the plasma enters the space, and creatinga component of magnetic field in said path in the same direction as saidconfining field to restore the confining field in said path after theplasma has entered the space.

2. A method according to claim 1 wherein the field suppressing stepcomprises momentarily creating a component of magnetic field in saidpath, which component is opposed to said confining field.

3. A method according to claim 1 wherein said confining field issuppressed for approximately 20 sec.

4. A method according to claim 1 including the step of synchronizingsaid plasma accelerating step and said field suppressing step so thatthe confining field is suppressed at the time that the plasma reachesthe space.

5. A method of injecting plasma into a space wherein a plasma confiningmagnetic field exists comprising the steps of accelerating the plasma ina path toward the space, and momentarily suppressing the confining fieldin the path of the plasma so that the plasma enters the space whereinsaid plasma confining magnetic field is produced by a first current in afirst conductor outside of the space, said conductor having an aperturein said path for the entry of plasma, and wherein said field suppressingstep comprises producing a second current flowing along an annularsecond conductor positioned adjacent the aperture in a directionopposite to the direction of current flow in said [first conductor.

\6. A method according to claim 5 wherein said annular conductorsurrounds the path of the plasma including causing said second currentto flow around said path to produce a longitudinal magnetic fieldforcing the plasma away from said second conductor.

7. A method of injecting plasma into a space wherein a plasma confiningmagnetic field exists comprising the steps of accelerating the plasma ina path toward the 1 space, momentarily suppressing the confining fieldin the path of the plasma so that the plasma enters the space, andcreating a component of magnetic field in said path in the samedirection as said confining field to restore the confining field in saidpath after the plasma has entered the space, including producing asubstantially closed sheet of current surrounding the path of the plasmato create a longitudinal magnetic field directed along said path toguide said plasma toward said space.

8. A method of injecting plasma into a space wherein a plasma confiningmagnetic field exists comprising the steps of accelerating the plasma ina path toward the space, momentarily suppressing the confining field inthe path of the plasma so that the plasma enters the space, andrestoring the confining field in said path after the plasma has enteredthe space so that the plasma is confined in the space wherein saidplasma confining magnetic field is produced by a current in a firstconductor outside of the space, said conductor having an aperture insaid path for the entry of plasma, and wherein said field restoring stepcomprises producing a current flowing along an annular second conductorpositioned adjacent the aperture in the same direction as the directionof the current flow in said first conductor.

9. A method of injecting plasma into a space wherein a plasma con-finingmagnetic tfield exists comprising the steps of accelerating the plasmain a path toward the space, and momentarily suppressing the confiningfield in the path of the plasma so that the plasma enters the spaceincluding the steps of passing current unidirectionally through a firstconductor, the current in said first conductor creating a plasmaconfining field in the space, thereafter shunting the first conductor sothat said current continues to pass therethrough, thereafter passingcurrent momentarily through a second conductor {in such direction as tocreate a component of magnetic field in said plasma path opposed to theplasma confining field, whereby the plasma confining field ismomentarily suppressed.

10. A method according to claim 9 wherein simultaneously with thepassage of current through said first conductor current is passedthrough said second conductor in a direction so as to create a secondcomponent of magnetic field in said plasma path in the same direction asthe plasma confining field created by the current in said firstconductor, whereby the plasma confining field is increased.

11. A method according to claim 9 wherein said first conductor has aninductance of such magnitude that said plasma confining field persistsfor a time which is long relative to the duration of said component ofmagnetic field opposed thereto.

12. A method of injecting plasma into a space wherein a plasma confiningmagnetic field exists comprising the steps of accelerating the plasma ina path toward the space, and momentarily suppressing the confining fieldin the path of the plasma so that the plasma enters the space includingthe steps of charging a first and second capacitor, thereafterdischarging said first capacitor through a first conductor so as to passa current unidirectionally therethrough, the current in said firstconductor creating a plasma confining field in the space, thereaftershort circuiting said first conductor when said capacitor issubstantially completely discharged so that said current continues topass through said first conductor, thereafter discharging said secondcapacitor through a second conductor in such direction as to create acomponent of magnetic rfield in said plasma path opposed to the plasmaconfining field whereby the plasma confining field is momentarilysuppressed.

13. A method according to claim 12 wherein simultaneously with thepassage of current through said first conductor current from said firstcapacitor is passed through said second conductor in a direction so asto create a second component of magnetic field in said plasma path inthe same direction as the plasma confining field created by the currentin said first conductor 'whereby the plasma field is increased, saidfirst conductor has an inductance of such magnitude that said plasmaconfining field persists for a time which is long relative to theduration of said component of magnetic field opposed thereto, saidsecond conductor having inductance of such magnitude that oscillation ofsaid current caused by discharge of said second capacitor is damped, andincluding the step of synchronizing said plasma accelerating step, saiddischarge of said first and second capacitors and said short circuitingof said first conductor so that the confining field is momentarilysuppressed at the time that the plasma reaches the space.

14. Apparatus for injecting plasma into a space wherein a plasmaconfining magnetic field is produced by a first conductor outside of thespace, Said first conductor having an aperture therein for the entry ofplasma, comprising means for accelerating plasma in a path toward thespace, said plasma path passing through said aperture, and fieldsuppressing means for momentarily suppressing the confining fieldadjacent said plasma path so that the plasma enters the space includingan annular second conductor insulated from the first conductor andpositioned adjacent the aperture around said plasma path.

15. Apparatus according to claim 14 including a first source of powerlinked with said first and second conductors, a second source of powerlinked with said second conductor, first switching means connectedbetween said first power source and said first and second conductors forcausing a first current to flow through each of said first and secondconductors so that the current through each of said conductors producesrespective first and second magnetic field components having the samedirection, second switching means for shunting the first power sourceand the first switching means so that said first current continues tocirculate through said first and second conductors, third switchingmeans for causing current to flow through said second conductor so thatthe current through said second conductor produces a third magneticfield component opposed to the magnetic field component produced by thecurrent in said first conductor, current damping means connected betweensaid second power source and said second conductor so that said thirdmagnetic field component decays rapidly relative to the decay of saidfirst and second magnetic field components, and timing means foractuating said first, second and third switching means at predeterminedtimes.

16. Apparatus according to claim 14 wherein said second conductor isconnected to an electrical power source on opposite sides of said plasmapath so that current divides and flows through said annular secondconductor around each side of plasma path.

17. Apparatus according to claim 16 wherein said second conductorcomprises two portions extending along the path of the plasma andinsulated from one another, including means for causing differentcurrents to flow in each of said portions so as to produce alongitudinal magnetic field forcing the plasma away from said secondconductor.

18. Apparatus according to claim 16 including means for causing thecurrent in said second conductor to flow momentarily in a directionopposite to the direction of current flow in the first conductor so thatthe plasma enters the space.

19. Apparatus according to claim 18 including means for causing thecurrent in said second conductor to flow in th esame direction as thecurrent in the first conductor so that the confining field is reinforcedadjacent the aperture.

References Cited UNITED STATES PATENTS 3,408,527 10/1968 Koller et a1.315-11l X 3,005,767 10/1961 Boyer et al. 3l5111 X 3,166,477 1/1965Leboutet 315111 X 3,194,739 7/1965 Kerst et al. 3l5l1l X 3,325,7136/1967 Seidl et al. 328233 JAMES W. LAWRENCE, Primary Examiner P. C.DEMEO, Assistant Examiner US. Cl. X.R.

Patent No. 9 Dated August a 1970 Inventor(s) Tihiro Ohkawa and Arthur A.Schupp It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 7, line 11, "12 inches" should read "2 inches.-

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FORM PO-IOSO (10-69) USCOMM-DC 60376-F'GD i UYS. GOVIINMENT PIINYINGOFFICE: Ill! 0-.6-384

